System for measuring turbulence remotely

ABSTRACT

A method of predicting turbulence that may involve receiving electromagnetic energy that has traveled along a path subject to the turbulence, with the turbulence altering the electromagnetic energy. A determination may be made as to the alteration caused by the turbulence by filtering the electromagnetic energy as it was received with a velocity of one of a transmitter of the electromagnetic energy or a receiver that received the electromagnetic energy.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional of U.S. patent application Ser. No.12/499,869, filed Jul. 9, 2009, which is a divisional of U.S. patentapplication Ser. No. 11/003,868, filed on Dec. 3, 2004 (now U.S. Pat.No. 7,598,901). The entire disclosure of the above applications isincorporated herein by reference.

FIELD

This disclosure relates generally to meteorological sensors and, moreparticularly, sensors that sense clear air turbulence remotely.

BACKGROUND

Clear air turbulence significantly affects the comfort of passengers oncommercial aircraft and has even caused some would be passengers toforego flying due to their fears associated with the turbulence. Becauseclear air turbulence can occur with little or no warning, the passengerstend to stay in their seats with their seat belts fastened. At times,though, every passenger must get up for comfort and physiologicalreasons. Therefore, if the aircraft must proceed through the turbulence,it would be useful if the aircrew could alert the passengers to thedisturbance before the aircraft encounters it.

Preferably, the aircraft would avoid the turbulence altogether but eventhat preventative measure requires that the turbulence be detected orpredicted before it occurs. While much turbulence (e.g. the turbulenceassociated with thunderstorms) can be predicted or detected, clear airturbulence can not be detected or predicted by currently availabletechnology. The reason that clear air turbulence cannot be detected isthat it consists of masses of air having slightly differenttemperatures, pressures, and densities moving at various speeds anddirections in the atmosphere. The minute differences in these air massesdo not reflect radar differently enough to make the radar return fromone mass of air distinguishable from the radar return from another massof air.

While meteorological maps provide flight crews some indication of whereturbulence might be expected, these maps are not perfect. First, theytend to become stale within hours and are based on underlyingmeteorological models that are far from perfect also. Additionally,turbulence occurs across a wide variety of geometric scales. Someturbulent areas can extend for many kilometers, or even hundreds ofkilometers (e.g. the turbulent region surrounding the jet stream). Otherareas of turbulence occur on the scale of kilometers or fractions ofkilometers such as the turbulence associated with the downstream side ofa mountain that is subjected to brief wind gusts of significantvelocity. Due to their scale, these smaller volumes of turbulence willnot appear on the meteorological maps.

In the absence of any better approach, the aviation industry has createda system in which the pilots of each aircraft radio in reports of theclear air turbulence that they encounter on their routes, or “airways.”Subsequent aircraft flying the same airway can maneuver in response tothese reports but risk encountering turbulence along their detour.Obviously, the first aircrew to fly along a given airway after theairway has been vacant for some time will have no reports on which tobase evasive action. Likewise, those aircraft on unplanned detours suchas when an airport is too busy to accept arrivals, or is otherwise shutdown (by for example severe weather), will have no way to foresee theturbulence along the route.

SUMMARY

In one aspect the present disclosure relates to a method of predictingturbulence. The method may include receiving electromagnetic energy thathas traveled along a path subject to the turbulence, with the turbulencealtering the electromagnetic energy. A determination may be made as tothe alteration caused by the turbulence by filtering the electromagneticenergy as it was received with a velocity, of one of a transmitter ofthe electromagnetic energy or a receiver that received theelectromagnetic energy.

In another aspect the present disclosure relates to a method ofpredicting turbulence. The method may include receiving electromagneticenergy that has traveled along a path subject to the turbulence, theturbulence altering the electromagnetic energy. The alteration caused bythe turbulence may be determined by filtering the electromagnetic energyas it was received with a velocity of one of a transmitter of theelectromagnetic energy or a receiver that received the electromagneticenergy. A three dimensional model of the turbulence may then be created.

In still another aspect the present disclosure relates a method ofpredicting turbulence. The method may comprise receiving electromagneticenergy that has traveled along a path subject to the turbulence, theturbulence altering the electromagnetic energy. The alteration caused bythe turbulence may be determined by filtering the electromagnetic energyas it was received with a velocity of one of a transmitter of theelectromagnetic energy or a receiver that received the electromagneticenergy. The velocity may include at least one of a linear velocity or anangular velocity. A direction may be determined between the receiver andthe transmitter. A three dimensional model of the turbulence may becreated.

Further areas of applicability will become apparent from the descriptionprovided herein. The description and specific examples in this summaryare intended for purposes of illustration only and are not intended tolimit the scope of the present disclosure.

DRAWINGS

The drawings described herein are for illustrative purposes only ofselected embodiments and not all possible implementations, and are notintended to limit the scope of the present disclosure.

FIG. 1 illustrates a global system for the detection of clear airturbulence in accordance with the principles of the present disclosure;

FIG. 2 schematically illustrates a radio receiver of a preferredembodiment of the present disclosure;

FIG. 3 illustrates a system architecture for the system of FIG. 1; and

FIG. 4 illustrates a method in accordance with the principles of thepresent disclosure.

Corresponding reference numerals indicate corresponding parts throughoutthe several views of the drawings.

DETAILED DESCRIPTION OF VARIOUS EMBODIMENTS

The present disclosure in one implementation relates to a system fordetecting turbulence along a path that is subject to turbulence. Thesystem may make use of at least one transmitter to transmitelectromagnetic (EM) energy along the path and at least one receiver toreceive the EM energy. At least one of the transmitter and the receivermoves along the path. The receiver may have an antenna responsive toincident EM energy to produce a received signal, and an input foraccepting a velocity signal indicating a velocity that the receiver orthe transmitter is moving at. The receiver processes the received signalusing the velocity signal to remove a shift associated with the receivedsignal because of relative motion between a source of the EM energy andthe receiver or transmitter that is moving along the path. Thus, thereceiver determines an alteration of the EM energy caused by theturbulence and outputs a signal indicative of the turbulence.

In another implementation the present disclosure relates to a system fordetecting turbulence along a path being traveled by a mobile platform.The system may include at least one transmitter to transmitelectromagnetic energy along the path, and at least one receiver locatedon the mobile platform to receive the electromagnetic energy as themobile platform travels along the path. The receiver may include anantenna responsive to incident electromagnetic energy to produce areceived signal, and an input to accept a velocity signal that isrepresentative of a velocity at which the one of the receiver and thetransmitter is moving along the path. The receiver is adapted to processthe received signal using the velocity signal to remove a shiftassociated with the received signal because of relative motion between asource of the electromagnetic energy and the one of the receiver and thetransmitter that is moving along the path. In this manner the receiverdetermines an alteration of the electromagnetic energy caused by theturbulence. The receiver is adapted to output a signal that isrepresentative of the turbulence.

In another aspect a system is disclosed for detecting turbulence along apath being traveled by a mobile platform. The system may include atleast one transmitter to transmit electromagnetic energy along the path,and at least one receiver located on the mobile platform to receive theelectromagnetic energy as the mobile platform travels along the path.The receiver may include an antenna responsive to incidentelectromagnetic energy to produce a received signal, and an input toaccept a velocity signal that is representative of a velocity at whichthe one of the receiver and the transmitter is moving along the path.The receiver is adapted to process the received signal using thevelocity signal to remove a shift associated with the received signalbecause of relative motion between a source of the electromagneticenergy and the one of the receiver and the transmitter that is movingalong the path. In this manner the receiver determines an alteration ofthe electromagnetic energy caused by the turbulence. The receiver isalso adapted to output a signal that is representative of theturbulence. A processor receives the output signal and creates a threedimensional model of the turbulence using the output signal.

Apparatus and methods for remotely sensing turbulence, particularly aclear air turbulence meter, provide a system that measures atmosphericturbulence along a line of sight between a receiver and a satellite. Thesystem uses alterations to a signal (that include, but are not limitedto changes in intensity, phase, and frequency) that is transmitted fromthe satellite to the receiver to make the turbulence measurement. In oneembodiment, the receiver is a GPS receiver that estimates thecontribution of ionospheric scintillation to the signal alterations byusing the GPS L1 and L2 bands. Preferably, these ionosphere effects areremoved from the alteration to isolate the effects of troposphericturbulence on the signal.

Other embodiments are adapted for use on land and marine vehicles andinclude velocity sensors such as inertial measurement units that enablethe receiver to adjust the turbulence measurement to account for themotion of the vehicle. In the alternative, the system can include aninput for receiving velocity information from the vehicle. Thesevehicle-adapted systems can determine velocity-induced phase shifts andDoppler effects from the velocity of the vehicle and remove theseeffects from the measured variations of the signal. Also, the system caninclude an input to receive the heading of the vehicle to enable thesystem to determine the direction to each GPS satellite currently inview. The direction can be determined relative to the aircraft headingor relative to the ground (or Earth). Further, the system can adjust themeasured turbulence estimate for crosswind effects (i.e. apparentturbulence introduced into the measurement because of the motion of thereceiver relative to the turbulent volumes of air). Moreover, signalsfrom more than one satellite constellation (e.g. GPS, GLONASS, andGalileo) can be used by the receiver to make the measurements. Usingmore than one constellation improves the availability of transmittedsignals, gives better coverage of the atmosphere, and improves theaccuracy of the turbulence measurements. The turbulence measurements canbe conveyed to end users such as the aircrew, air traffic controllers orcomputers, or other aircraft. The forms in which the turbulencemeasurements can be conveyed include audible alarms, overlays ofturbulence intensity on aircrew station displays, or overlays ofturbulence intensity on a map. Thus, airlines operating in accordancewith the principles of the present disclosure will provide smootherflights with fewer occurrences of passengers being advised to return totheir seats because of the possibility of turbulence. Moreover, thenumber of times when the advisories are based on inaccurate predictions(e.g. “false alarms”) wilt be reduced. Likewise, detours of aircraftaround turbulence will be avoided thereby reducing fuel consumption.

In a second embodiment, the present disclosure provides a receiver ofelectromagnetic energy (that travels along a path that is subject toturbulence). The receiver includes an input, an output, and a circuit incommunication with the input and the output. The input receives a firstsignal that is representative of the electromagnetic energy as it isreceived. The circuit accepts the first signal and a second signal thatis representative of a velocity of a mobile platform. Also, the circuitadjusts the first signal using the second signal to determine analteration of the electromagnetic energy caused by the turbulencethereby eliminating alterations caused by the velocity of the mobileplatform. In one embodiment the circuit determines the alteration causedby only the tropospheric turbulence. The output generates a third signalthat is representative of the turbulence.

The receiver may include a GPS (Global Positioning System), or similarcircuit, and accepts a fourth signal that is representative of a headingof the mobile platform. From the fourth signal, the receiver determinesa direction to the source of the electromagnetic energy. Moreover, thecircuit may accept yet another signal that is representative of theelectromagnetic energy from a second receiving location. In theseembodiments, the circuit determines from that signal a second alterationof the energy caused by the turbulence. In another embodiment, thecircuit correlates the two measurements of the alteration caused by theturbulence. More particularly, the receiver correlates the twomeasurements with respect to the time it took for an antenna at thesecond location to move to the first location.

In a third embodiment the present disclosure provides a mobile platformthat includes an antenna, a velocity sensor, and an electromagneticenergy receiver. The antenna receives the electromagnetic energy (thathas traveled along a path subject to turbulence) while the sensor sensesthe velocity of the mobile platform. Using the sensed velocity, thereceiver filters the as-received electromagnetic energy to determine analteration to the energy that was caused by the turbulence. The mobileplatform may also provide to the receiver a signal representing aheading of the platform so that the receiver can determine a directionto the source of the energy. Also, the mobile platform (e.g. anaircraft, a land vehicle, or a marine vehicle) can include a secondantenna to receive the electromagnetic energy thereby allowing thecircuit to make a second measurement of the turbulence. Additionally,the circuit may correlate the two measurements with respect to theamount of time it took for the second antenna to move to the locationwhere the first antenna received the energy. Preferably, the antennasare located on a sidewall of the mobile platform.

In another embodiment the present disclosure provides a system fordetecting turbulence. In this current embodiment the system includes atleast one mobile platform, a sensor that determines the velocity of theat least one mobile platform, at least one electromagnetic energytransmitter, and at least one receiver. The transmitter transmits theelectromagnetic energy across a path that is subject to turbulence andthe receiver receives the energy (even if the transmitter is near thehorizon as seen by the receiver). At least one of the transmitters orreceivers is on the mobile platform. Again, the receiver determines analteration to the energy that is caused by the turbulence. When thereceiver determines the alteration the receiver may also associate atime, a location, and a direction with the determined alteration.Preferably, the system includes a processor that creates a threedimensional model (e.g. a computer aided tomographic model) of theturbulence from the measurements made by the receivers. In turn, anetwork may be used to distribute the model to subscribers in apublish-subscribe architecture. In another preferred embodiment themodel includes a statistical confidence interval. Moreover, the modelmay be supplemented with data from other sources such as air datasensors, inertial sensors on mobile platforms, meteorological sensors,and meteorological predictions. The system may be configured to sensethe turbulence over a pre-selected geographic region such as an airportapproach or departure path.

A method of measuring turbulence is also provided. The method in oneform may include receiving electromagnetic energy that has traveledalong a path subject to the turbulence. The method may also includedetermining the alteration to the energy caused by the turbulence byfiltering the electromagnetic energy (as it was received) with a signalthat represents the velocity of either the transmitter or the receiver.An alteration caused by the ionosphere may also be filtered from thealteration to the electromagnetic energy. The method may includedetermining a direction between the receiver and the transmitter. Adetermination may also be made of the alteration caused by theturbulence as measured at a second location. Further, athree-dimensional model of the turbulence may be created and distributedto subscribers to the model.

It will be appreciated that many modern aircraft use radio positioningsignals broadcast from satellites (e.g. GPS or GLONASS) for navigation.Atmospheric turbulence can cause the GPS receivers to occasionally loselock with the signals by corrupting, or altering, the signal to anextent sufficient to render the receiver temporarily inoperative. Theproblem becomes more pronounced when the transmitting satellite, as seenby the receiver, nears the horizon. Not only does the signal have totraverse a significantly longer path through the atmosphere, but thesignal path is likely to penetrate deeply into the troposphere whereturbulence can be much more pronounced than in the higher portions ofthe atmosphere. Also, as the signal path nears the ground, multipathingcan occur which further degrades the signal quality. Because turbulencehas previously been seen as a problem to be avoided, the receiverantennas are typically configured to reject signals with low elevationangles relative to the horizon.

According to the principles of the present disclosure, though, thealtered signals carry an indication of the amount of turbulence throughwhich the signals have passed. While any one signal only conveysinformation regarding the turbulence along its path, the large number ofGPS receivers and satellites currently in use provide a plethora ofturbulence measurements along the numerous paths between these devices.By a process similar to tomography (e.g. computer aided tomography orCAT), these turbulence measurements can be used to create athree-dimensional model of the turbulence in the atmosphere.

Before turning to a more detailed description of the disclosure, it isuseful to discuss the structure of the atmosphere as it relates toturbulence. The lowest portion of the atmosphere is the troposphere andis the volume of air where most commercial and military aviation occurs.The troposphere begins at the surface of the Earth and, during the day,is composed of a surface boundary layer, a mixing layer, an entrainmentlayer, and the lowest reaches of the “free” atmosphere. The surfaceboundary layer, mixing layer, and entrainment layer typically extend upto about 1 to 3 kilometers. These layers are sometimes collectivelyreferred to as the planetary boundary layer because effects offrictional drag with the surface of the Earth can be observed in theselayers. In contrast to these lower levels of the atmosphere, the effectsof the ground are negligible, or nonexistent, in the “free” atmosphere.

Because it is the layer of the atmosphere in direct contact with theEarth, the surface boundary layer (which is about 10% of the planetaryboundary layer) is dominated by mechanical shear between the air and theground and outright obstructions to the movement of the air (e.g.mountains or buildings). These interactions give rise to local eddies onmany scales from millimeters to many hundreds of kilometers. Solarheating and radiative cooling of the air and the ground cause areas ofconvection to develop thereby creating up and down drafts. Thus, winds(i.e. the turbulence) in the surface boundary layer have components inall three dimensions and are not a function of height. Further, strongvertical gradients exist in the properties (e.g. temperature, pressure,and humidity) of the air in this layer.

Being above the surface boundary layer, the mixing layer is influencedby the ground to a lesser extent than the surface boundary layer. Thewinds in the mixing layer are characterized by large scale eddies thatare generally on the scale of many kilometers, or larger. Additionally,plumes of heated air rising from the surface boundary layer and massesof cooler air sinking from the entrainment layer (i.e. tubules) alsoexist in a generally random distribution throughout the mixing layer.Thus, much of the small-scale chaotic flow of the surface boundarydissipates with altitude.

The entrainment layer lies just above the mixing layer. In theentrainment layer, the rising plumes of heated air reach thermodynamicequilibrium with their surroundings and stop rising. Cumulus cloudstherefore form at the tops of these thermal plumes which can reach thetop of the troposphere in extreme cases (e.g. severe thunderstorms).Adjacent to the warm rising plumes of air, masses of cooler denser airare displaced and sink into the mixing layer.

At night heating from solar radiation stops as radiative cooling of theground and air begins to predominate. Thus, the energy that drives thedaytime turbulence fades and allows friction with the surface tostabilize a layer of air near the ground. Another layer of air above the“stable layer” contains residual turbulence left behind by the daytimeatmosphere. The “residual” layer generally corresponds to the mixing andentrainment layers.

Thus, in general, turbulence occurs when the cells of air in the mixinglayer, called turbules, rise and fall through the atmosphere atdifferent rates due to density differences between the turbules and thesurrounding air. Sometimes the turbulence is visible, or detectable withradar, due to precipitation entrained in (or precipitating from) theturbulent air. Often, though, no detectable indication of the turbulenceoccurs so that when an aircraft encounters the turbulence, it appears tocome from the “clear air.”

The density differences between the turbules and surrounding air arelargely a function of temperature, pressure, and humidity although otherproperties of the air in the turbule also vary from that of thesurrounding air. Because of the differing properties, the index ofrefraction of the air in the turbules differs from the index ofrefraction of the nearby air in the mixing layer. Ao has shown that theindex of refraction “n” is related to the properties of air as follows:(n−1)×10⁶ =a ₁ P/T+a ₂ P _(w) /T ²where T is the air temperature, P is the air pressure, P_(w) is thewater vapor pressure (i.e. a measure of humidity), a₁ is 77.6 K mbar⁻¹and a₂ is 3.73×10⁵ K² mbar⁻¹. [Ao, C. O. et al., Lower-TroposphereRefractivity Bias in GPS Occultation Retrievals, Journal of GeophysicalResearch, 108 (D18), Pages 1-12.] As a result, the turbules refractelectromagnetic waves as the waves pass through the turbules. The amountof refraction occurring along a wave's (or signal's) path thereforechanges as turbules move into or out of the signal path. The changingamount of refraction causes several measurable alterations to thesignal. More particularly, these alterations include changes in thephase, the intensity, and the frequency of the wave induced by changesto the path that the signal travels.

Moreover, because the signal path is continuously changing, the signalwill appear to be arriving from different paths. Because the paths havedifferent lengths, it is possible for one instantaneous portion of thewave to partially overtake another instantaneous portion of the wavesignal. Thus, the portions of the wave may interfere eitherconstructively or destructively. The result is higher or lower signalintensity, respectively, at the receiver. Thus, rapid variations inintensity are therefore an indicator of turbulence along the signalpath.

The changing signal paths also give rise to frequency shifts of thesignal. These frequency shifts occur because the effect of the changingpath lengths is the same as if the satellite were actually retreating atthe velocity with which the path length changes. This phenomenon issimilar to the Doppler effect caused by a transmitter and receivermoving relative to each other. Thus, rapid changes in frequency alsoindicate turbulence along the signal path. Previously available GPSreceivers typically measure frequency and use the detected Dopplereffect to compute the receiver's heading and speed. However, theseprevious GPS receivers, by design, smooth out short-term fluctuations togive an accurate average receiver velocity. Thus, the previouslyavailable GPS receivers treat the fluctuations as a problem whereas thereceivers of the current embodiment include frequency detectors thatpick up the signal prior to the averaging function and provide anotherindication of turbulence.

Turning now to the phase shifts caused by the turbules, these shiftsalso occur because at one instant the signal arrives from one path andat the next instant it arrives from a slightly different path. Becausethe different paths will almost always have different lengths, thesignal arriving at one instant will have traveled a different distancethan the signal arriving at another instant. The difference in pathlength causes the signal to undergo a phase shift at one time relativeto the other time. Thus, variations in phase are yet another indicatorof turbulence along the signal path.

Tropospheric turbulence is not the only source of alteration to (i.e.scintillation of) signals transmitted to, or from, space. The Earth'sionosphere also alters the signals in a manner that is stronglydependant on frequency. Thus, the receivers of the present disclosureuse signals having different frequencies to measure the ionosphericeffects on the signals. As a result, the receivers can remove theionospheric alterations from the signals thereby leaving only thealterations that are due to tropospheric effects (i.e. troposphereturbulence).

In a preferred embodiment the disclosure combines the use ofhigh-quality GPS receivers onboard aircraft to measure signal qualitywith a computerized navigation system to compute the relative positionsof the aircraft and satellites. The receivers use the GPS signal qualityto estimate turbulence between the aircraft and the satellites. Ifstrong turbulence is detected in an aircraft's path, a warning may beissued to the aircrew. Otherwise, the turbulence measurements can becollected and used to build a three dimensional model of the atmospherethat shows where turbulence is occurring and the degree to which it isoccurring.

Referring to the accompanying drawings in which like reference numbersindicate like elements, FIG. 1 illustrates a global turbulence measuringsystem 10 constructed in accordance with the principles of the presentdisclosure.

The exemplary system 10 shown in FIG. 1 includes a constellation ofsatellites 12, 14, 16, 18, and 20, a plurality of mobile platforms 22,24, and 26, and a ground station 28 distributed in such a manner as todetect the volumes of turbulence 30 that might occur in the atmosphere.While the turbulence 30 is shown as a cumulonimbus cloud (i.e. athunderstorm) the principles of the present disclosure apply equallywell to turbulence that bears no visible indication of its presence andto turbulence that cannot be detected by radar. Also, FIG. 1 shows thetroposphere 32 (extending up to an altitude of about 11 miles) and theionosphere 34 (extending up to an altitude of about 400 miles).

The satellites 12, 14, 16, 18, and 20 may be any satellite thattransmits signals in the form of electromagnetic energy (e.g. radiofrequency energy) generally toward the Earth or any other celestial bodyhaving an atmosphere. Preferably, the satellites are components of aconstellation of satellites such as a system for providing globalpositioning services (e.g. the Global Positioning System, GLONASS, orGalileo systems), a system for providing telecommunications (e.g. theIRIDIUM®, GLOBALSTAR®, Intermediate Circular Orbit (ICO®), ORBCOMM®, orTELEDESIC® satellite communication systems), or even a collection ofunrelated satellites. Likewise, the particular mobile platforms 22, 24,and 26 used are not critical. But exemplary mobile platforms includeaircraft 22 and 24 and ships 26 as well as other air, space, marine, andland vehicles. Preferably, each satellite carries a transmitter tobroadcast signals for receipt by receivers at the terrestrial portions22, 24, 26, and 28 of the system 10 although the location of thereceivers and transmitters can be reversed or interchanged withoutdeparting from the scope of the present disclosure.

The transmission of the signals between the transmitters and receiversis illustrated by a variety of signal paths in FIG. 1. For instance,satellite 12 is shown transmitting two signals received by the aircraft22 and one signal received by the ship 26 via, respectively paths 36, 38and path 40. Satellite 14 is also shown transmitting to the aircraft 22via path 42. Likewise, satellite 16 is transmitting to the aircraft 24via path 44 and satellite 18 is transmitting to the ship 26 via path 46.As is apparent from FIG. 1, each of the receiving portions of the system10 can receive one, or more, signals.

The majority of these paths 36, 38, 40, 42, 44, and 46 will pass throughboth the ionosphere 34 and the troposphere 32 while being altered byconditions in each of these portions of the atmosphere. Thesealterations will typically include instant-to-instant phase shifts,frequency shifts, and intensity changes in the signal as it is receivedat the terrestrial portions 22, 24, 26, and 28 of the system 10. Manyportions of the system 10 move. Thus, the paths 36, 38, 40, 42, 44, and46 will sweep through the atmosphere forming curvilinearthree-dimensional surfaces along which the signals travel during thetime that any pair of transmitters and receivers are visible to one andother. As the mobile components of the system 10 move, the paths willencounter varying degrees of turbulence 30. For example, paths 36, 38,40, and 24 are shown traversing relatively stable portions of theatmosphere while paths 42 and 46 are both shown penetrating the volumeof turbulence 30 albeit at different locations and angles. Thus, theturbulence 30 will alter the signals traveling on the paths 42 and 46 toa greater extent than the atmosphere will alter the signals that travelon the other paths 36, 38, 40, and 44.

With reference now to FIG. 2, a receiver 110 constructed in accordancewith a preferred embodiment of the present embodiment is illustrated inblock diagram form. For perspective, a simplified system 100 is alsoshown and includes a satellite or transmitter 106 broadcasting a signal108 to the exemplary receiver 110. The receiver 110 includes a number ofinputs, outputs, and components as follows: a transmitted signal input112, a signal rejector 114, a signal bypass 116, a signalconditioner/demodulator 118, a phase detector 120, a frequency detector122, an amplitude or intensity detector 124, and a signal processor 126.The receiver 110 also includes an ionospheric turbulence detector 132, arelated inverter 134, and a signal direction finder 136. To interfacewith systems onboard a mobile platform, the receiver 110 also includes amobile platform systems input 127, a phase shift estimator 128, afrequency shift estimator 130, and a pair of related inverters 129 and131. The components of the receiver 110 (and their equivalents) areinterconnected with each other as shown or can be implemented insoftware. Further, the receiver 110 communicates with one, or more,antennas 138 via the input 112 to receive the signals from the satellite106. Also, the receiver 110 communicates with the INS (InertialNavigation System) and FCS (Flight Control System) 140 of the mobileplatform via the input 127. As will be described, the receiver 110generates a turbulence vector at an output 142.

In operation, the transmitter 106 transmits an electromagnetic signal108 that travels along a path that is subject to turbulence. Theturbulence alters the signal 108 thereby causing phase shifts, frequencyshifts, or changes to the intensity (i.e. fading and enhancement) of thesignal as it is received at the antenna 138. The antenna 138 guides thesignal to the signal input 112. If the transmitter 106 is too close tothe horizon, an antenna properly designed for positioning applicationswill typically reject the signal 108 due to the possibility that noisemay corrupt the incoming signal. This feature is shown schematically atthe rejector 114 even though no component that is separate from theantenna 138 is usually required. The present disclosure seeks theselow-elevation, noisy signals 108, in particular, because they bearuseful indications of the turbulence 30 (see FIG. 1) along the signal's108 path through the atmosphere. Thus, the bypass 116 schematicallyshows the antenna 138 communicating all signals 108 to the signalconditioner 118 even though the signals 108 may be close to the horizon.Again, the bypass function 116 for the noisy signals is typically acharacteristic of the antenna 138 rather than a component separate fromthe antenna 138.

The signal conditioner 118 of FIG. 2 could be divided into two portions:one portion for conditioning the relatively noise-free signals andgenerating position data and another portion conditioning all signalsand supporting the generation of turbulence data. At appropriate nodeswithin the signal conditioner 118, signals are picked up andcommunicated to the detectors 120, 122, and 124. By examining the signal108, the detectors 120, 122, and 124 detect, respectively, phase shifts,frequency shifts, and fading or enhancement of the signal 108. Themagnitude of these alterations and the rates at which they are detectedare fed to the signal processor 126 (or an equivalent analog circuit)that converts the data to an indication of the amount of turbulencealong the path that the signal 108 took in reaching the antenna 138.Generally, the turbulence will be proportional to a combination of thealterations to the signal 108 caused by the turbulence.

Adjustments may also be made to the turbulence measurements made by thereceiver 110 to account for the motion of the mobile platform (i.e. theantenna 138) and for ionospheric effects on the signal 108. The motionof the antenna 138 is caused by a combination of the velocity of themobile platform (in any combination of the x, y, and z dimensions) aswell as the rotation of the mobile platform about its roll, pitch, andyaw axes. Thus, the received signal may include alterations(particularly phase and intensity variations) caused by the motion ofthe antenna 138. Accordingly, the INS/FCS system 140 provides thereceiver 110 a signal that conveys the 6 degree of freedom (6 DOF)motion of the mobile platform to the receiver 110 via the input 127. Aphase shift estimator 128 and a frequency shift estimator 130 act on thevelocity data to determine the phase and frequency alterationsintroduced into the received signal because of the mobile platformmotion. More particularly, the steady-state linear velocity of theaircraft 122 and the associated Doppler effect is easily determined bythe frequency estimator 130. Because the steady state velocity isrelatively constant, any phase difference introduced by the steady statevelocity generally will contribute little to the measured turbulence inthis manner. To the extent that the mobile platform velocity causes aphase shift, though, the phase shift is determined from the velocity bythe phase shift estimator 128. Similarly, the phase shift estimator 128determines the phase shift caused by the acceleration of the mobileplatform. Again, the phase difference arises because the signal arrivingat one instant travels a slightly different distance than a signalarriving at the next instant, with the distance changing in accordancewith the acceleration. Thus, the phase of the signal appears to shift byan amount determined by the travel of the mobile platform between thearrival of the signals at the different times.

In contrast to the linear velocity of the aircraft, the rotationalvelocity is subject to more rapid changes. These angular accelerationsarise from several sources including control inputs, local turbulenceexperienced directly by the aircraft, and aerodynamic forces acting onthe aircraft. Thus, the phase and frequency shift estimators 128 and 130use knowledge of the antenna locations and orientation on the aircraftalong with the sensed rotational motion to determine the Doppler andphase shifts caused by the instantaneous linear velocity andacceleration arising from the rotation. The inverters 129 and 131 invertthe resulting signals and communicate the result to the processor 126.The processor 126 then adjusts the signals that convey the magnitudesand rates of the alterations generated by the phase, frequency, andintensity detectors 120, 122, and 124 to remove the alterations causedby the motion of the antenna 138. The adjustment of the signal can be byway of, for example, a filtering algorithm. The adjusted magnitude andrate signals are then converted by the processor 126 to a measurement ofthe turbulence along the signal 108 path through the atmosphere.Accordingly, the processor 126 of FIG. 2 generates a measurement of theturbulence that is corrected for the motion of the antenna 138.

In addition to the alterations induced in the signal by troposphericturbulence, the ionosphere also alters the signal via interactionsbetween the signal and the charged particles in the ionosphere. Becauseionospheric scintillation is strongly frequency dependent, theionospheric scintillation detector 132 can, by comparing the L1 and L2GPS signals 108 (recall that the GPS system uses one signal at the L1frequency of about 1575 MHz and another signal at the L2 frequency ofabout 1228 MHz) to detect the amount of scintillation introduced intothe signal 108 by the ionosphere. The inverter 134 inverts the outputfrom the ionospheric scintillation detector 132 and communicates theinverted signal to the processor 126. The processor 126 uses theinverted ionospheric scintillation signal to remove the effects of theionospheric scintillation from the turbulence estimate. Thus, theprocessor 126 generates a signal indicative of the troposphericturbulence encountered by the signal 108 that is filtered of the effectsof the antenna motion and of the ionosphere.

Ionospheric scintillation is relatively constant with respect toelevation angle (i.e. the apparent height of a satellite above thehorizon) whereas tropospheric scintillation varies strongly withelevation angle. This relationship between elevation angle andtropospheric scintillation is an inverse relationship. Accordingly,ionospheric scintillation predominates at high elevation angles andtropospheric (turbulence induced) scintillation predominates at lowelevation angles. Thus, in a preferred embodiment, the antennas 138 andreceivers 110 are adapted to accept low elevation angle (less than aboutthe 5 degree default mask angle of the GPS system) signals.

At the next stage of the receiver 110 (as illustrated in FIG. 2),additional information is associated with the turbulence measurement. Inparticular, the direction finder 136 receives heading and orientationinformation from the mobile platform INS/FCS system 140 via the input127. Additionally, the direction finder 136 receives information fromthe signal conditioner 118 regarding which antenna 138A or 138B receivedthe signal 108 and which satellite 106 generated the signal. Theseantennas 138A and 138B correspond to the two antennas 23 and 25 on theaircraft 22 of FIG. 1. Knowing the location of each antenna on theaircraft 22 and the orientation of the antenna relative to the aircraft,the direction finder 136 determines the direction to the satellite 106that transmitted the signal 108 received by the antenna 138A or 138B.The direction finder 136 of the current embodiment associates thedirection and the time that the signal 108 was received with theturbulence measurement which, it receives from the processor 126.Accordingly, the output generated by the direction finder 136 is a timevarying vector defined by the amplitude of the turbulence measurement(from the processor 126) and the direction (in three dimensions) foundby the finder 136. This turbulence vector reflects the total amount oftropospheric turbulence along the signal 108 path at the time of thesignal's 108 receipt.

FIG. 1 also shows another preferred embodiment that includes theaircraft 22 which has three antennas 23, 25, and 27. Each of theantennas communicates with a receiver, such as the receiver 110 of FIG.2, for the measurement of turbulence. As shown, the aircraft 22 isflying toward the right and has the antenna 23 and 25 spaced apart fromeach other by a distance generally in the direction of the aircraft'svelocity. The antennas 23 and 25 are preferably on the sidewalls of theaircraft 22 and look abeam from the aircraft 22. The antenna 27 islocated at the nose of the aircraft 22 and faces forward along thedirection of travel. As the aircraft 22 moves, the paths 36 and 38between the antennas 23 and 25 and the satellite 12 also move while thereceiver 110 continues making turbulence measurements. As the paths 36and 38 move, the paths move into, through, and out of the various areasof turbulence 30 in the atmosphere. In contrast, because the antenna 27looks forward, the paths leading to the antenna 27 from most satelliteswill move very little as a result of the aircraft's motion (althoughthey will shorten as the aircraft moves toward the satellite).Accordingly, the side facing antennas 23 and 25 will receive signalsthat have more apparent turbulence induced variations than the signalsreceived by the forward facing antenna 27.

Over a period of time Δt, the aircraft 22 moves by a certain distancefrom the location where the leading antenna 25 received the signal alongpath 38 to a location where the trailing antenna 23 receives the signalalong the path 36 which is located where path 38 was located. For anantenna separation of about 10 meters at a typical aircraft cruise speedof 200 meters per second, Δt is approximately 50 milliseconds. Turbuleslarge enough to cause measurable changes in the GPS signal typicallyvary on a much slower time scale. Thus, aside from changes in theturbules themselves, the trailing antenna 23 will receive the signal atthe end of the period Δt with approximately the same alterations made toit by the turbules that (previously) the leading antenna 25 received atthe beginning of the period Δt. That is, the measurement of turbulencemade by antenna 25 along path 38 will be about the same as themeasurement of turbulence made by the antenna 23 along path 36.

In reality, various error sources will likely cause mismatches betweenthe measurements made by the two antennas 23 and 25. However, most ofthe error sources will either be truly random (e.g. thermal noise in thereceiver 110) or they will be common to both antennas (e.g. timingvariations aboard the GPS satellite). In the latter case, the errorswill be simultaneous but will occur at different locations. That is,simultaneous errors common to both antennas 23 and 25 will affect themeasurement made by antenna 23 along path 36 and will affect themeasurement made by antenna 25 along path 38. During both the previousand subsequent measurement cycles, the measurements along both paths 36and 38 will likely be unaffected.

To eliminate the random and common mode errors, the receiver 110correlates the two time-sequences of data resulting from themeasurements made by the two antennas 23 and 25. One of the twotime-sequences includes the samples of turbulence-related data (e.g.amplitude changes, phase shifts, or frequency shifts) from the leadingantenna 25. The other time-sequence of turbulence data is collected fromthe trailing antenna 23 and delayed with respect to samples in the firstsequence taken at the same location by Δt. Accordingly, the magnitude ofthe coefficient of correlation, r(Δt), for these two time-sequences ismaximized for parameter changes caused by turbules on the scale of thespacing between the two antennas 23 and 25. The correlation coefficientwith Δt≠0 also minimizes the effect of random errors in the two sets ofdata.

In a preferred embodiment, the receiver 110 of FIG. 2 continuouslydetermines the coefficient of correlation, r(Δt), and provides an outputsignal proportional to r²(Δt). This output can be used as an indicatorof turbulence along the line of sight to the satellite and is morerobust against error than an indicator based on a single antenna (e.g.antenna 23 alone). In other preferred embodiments, the disclosureprovides more than two GPS antennas along the length of a largeaircraft. Because many aircraft already have redundant antennas, littleor no equipment need be added to these aircraft. In these embodiments,the receiver 110 computes a coefficient of correlation for themeasurement data sets obtained by all of the antennas. The time-sequencefor each antenna is delayed by an appropriate interval so that all datasets cover the same signal path.

In another alternate embodiment, the disclosure uses signals fromsatellites other than those satellites that are designed to provideprecise navigation signals. Examples include communication and weathersatellites. Candidate communication satellites include the satellites inthe IRIDIUM® satellite constellation, the GLOBALSTAR® satelliteconstellation, the ICO® satellite constellation, and similarconstellations. One of the advantages of using these satellites is thatthey are more numerous than positioning satellites so they provide morefrequent opportunities to measure turbulence along a particular line ofsight or above a particular region. For embodiments using communicationssatellites it is preferred that the receiver correlate the signals fromtwo or more antennas so as to reject variations in the phase andfrequency of the transmitted signals that can be caused by timing errorsin the satellites' clocks.

With reference now to FIG. 3, another system 200 constructed inaccordance with the principles of the present disclosure is illustrated.FIG. 3 differs from FIG. 2 by generally showing how the system 200distributes and uses the turbulence vectors generated by the receivers210 whereas FIG. 2 generally illustrates how the receivers 110 generatethe turbulence vectors. Briefly, the transmitter 206 transmits signalsto the antennas 238. Systems 240 on the mobile platforms provide thereceivers 210 with information regarding the mobile platforms' velocity,heading, and orientation. From these signals, the receivers 210 generatethe turbulence vectors while, preferably, adjusting the as-receivedsignals for the velocity of the mobile platforms on which the receivers210 are situated. FIG. 2 also illustrates the receivers 210 providingseparate signals 254, 256, 258, and 260 carrying information pertainingto, respectively, the ionospheric scintillation, the troposphericturbulence, the correlation between different measures of thetropospheric turbulence, and the directions in which each of theturbulence measurements was made.

FIG. 3 also shows several additional aspects of the current embodimentincluding a network 262, a computer or processor 264, a meteorologicalprediction model 265, a set of air data sensors 266, a set ofmeteorological sensors 268, a set of inertial sensors 270, and apopulation of subscribers 272 that includes the Air Traffic ControlSystem 274. The processor 264 receives the numerous turbulence vectorsand related information over the network 262 which may include anairborne network such as the CONNECTION BY BOEING^(SM) system. From theturbulence information, the processor 264 creates a three-dimensionalmodel of the turbulence measured by the numerous receivers 210.Preferably, the processor 264 executes a tomography algorithm on thecollection of turbulence vectors to yield the three-dimensional model.

Tomography is a set of processes for determining the two-dimensional orthree-dimensional distribution of a quantity from a set of measurementsof that quantity taken along paths through an object or volume. Typicalproducts of tomographic processes include cross sectional depictions ofthree dimensional objects. An example of tomography is ComputerizedAxial Tomography (CAT), the basis of medical CAT scans. During a CATscan, the quantity measured is x-ray absorptivity as a proxy for tissuedensity. The CAT scan measures total x-ray absorption along each of manypoint-to-point lines through the patient's body. The tomographicalgorithm uses the collection of these one-dimensional x-ray absorptionmeasurements to estimate the x-ray absorptivity at many points insidethe body. Then, the CAT scan machine displays those measurements in atwo-dimensional depiction or a three dimensional, electronic model ofthe structures that absorbed the X-ray.

Referring again to FIG. 1, each of the paths 36, 38, 40, 42, 44, and 46represents a single, one-dimensional measurement of the turbulence 30 inthe atmosphere. These measurements may be adjusted to remove the effectsof ionospheric scintillation and the movement of the transmitter orreceiver. Also, the transmitting satellites 12, 14, 16, 18, and 20 andmobile platforms 22, 24, and 26 shown move thereby causing the signalpaths to sweep through the atmosphere. The movement of the paths 36, 38,40, 42, 44, and 46 allows many measurements of the turbulence 30 for anypair of one transmitter and one receiver. It should also be noted thatthe paths (not shown) between the ground station 28 represent a specialcase in which the paths move but pivot around one fixed end at theground station 28. Since the turbulence 30 moves and evolves at a slowerrate than the rapidly moving satellites 12, 14, 16, 18, and 20 andmobile platforms 22, 24, and 26, the measurements will remain valid forsome time after they are taken. Further, since approximately 5,000aircraft are aloft during a typical peak hour of flight time in theUnited States alone, and since there are at least 4 GPS satellitesvisible from any location, the system of FIG. 1 allows multiples of20,000 measurements of the turbulence 30 over the United States duringthe hours of most interest for detecting turbulence 30. This roughestimate does not include many types of potential receivers (e.g.handheld receivers, marine vehicles, land vehicles, stations, and theirequivalents) and many types of potential transmitters (e.g. otherpositioning system satellites, communication satellites and theirequivalents) so the actual number of potential measurements issubstantially greater the 20,000. All of these receivers (i.e. samplingnodes) are in communication with the processor 264 via the network.Since the processor 264 communicates via the network 262 its location isnot critical and could even be onboard one of the mobile platforms orsampling nodes.

In operation, each sampling node continuously measures the troposphericturbulence 30 along the line of sight from the node 22, 24, 26, or 28 toone, or more, of the transmitting satellites 12, 14, 16, 18, and 20. Thesampling nodes 22, 24, 26, or 28 transmit their one-dimensionalturbulence measurements, including the locations, directions, and timesassociated with each measurement to the processor 264. To build themodel, the processor 264 examines the set of measurements and identifiespoints, or volumes, where turbulence 30 is present. FIG. 1 shows howthis process operates on a relatively small sample of measurements. Asillustrated, many of the paths 36, 38, 40, and 44 will miss any giventurbule 30 in the atmosphere. However, other paths 42 and 46 willintersect the turbule 30 resulting in corresponding measurements thatwill be marked by a high degree of scintillation. By examining each ofthe many pairs of paths 36, 38, 40, 42, 44, and 46 to determine whetherthey intersect (or nearly intersect) and whether both paths exhibit highturbulence, the processor 264 identifies volumes of turbulence 30 at theintersection, or “near” intersection, of the pair of paths (here paths42 and 46). A near intersection means that the paths do not necessarilyintersect, but rather, pass within a distance from each other on thescale of the turbules 30 of interest. Once a path intersection with highindications of turbulence on both of the paths is identified, additionalpaths that come near the first intersection can be examined to improvethe identification and measurement of the turbulence 30. Other pathsthat intersect either of the first pair of intersecting paths 42 and 46can be examined to confirm that the measured turbulence actually occursat the intersection within the turbulence 30 rather than somewhere elsealong one of the intersecting paths 42 and 46. In other words, the factthat path 44 (for example) intersects path 46 but does not indicateturbulence, can be used to confirm that it is the intersection of path46 with path 42 about which the turbulence 30 can be found. In apreferred embodiment, a program for creating the model is stored on acomputer readable medium. The medium can be ROM, RAM, a hard drive, aCD, a floppy disk, flash memory, EPROM, mass storage, a network overwhich the program is transmitted, or any of their equivalents.

The sample of paths 36, 38, 40, 42, 44, and 46 shown in FIG. 1 isrelatively small but represents a much larger number of paths that wouldpreferably be used. However, the mobility of the transmitting satellites12, 14, 16, 18 and 20 and sampling nodes 22, 24, 26, and 28 allows alarge number of measurements to be made near the intersection of the twopaths 42 and 46 because the paths 42 and 46 move while the multiplemeasurements are made. Further, because the paths 42 and 46 willcontinue to intersect the turbulent volume 30 for numerous measurementsalong each path 42 and 46, the processor can identify the location ofthe turbule 30 by comparing the paths 42 and 46 in the time periodduring which they neared each other (and the turbule 30 also). Thus,when the processor detects an intersection of paths each having highturbulence, the processor can confirm the existence of a turbule 30 andits location by looking backward (and forward) along the time series ofmeasurements associated with the intersecting paths 42 and 46. As aresult, the present disclosure allows for a rapid initial localizationof turbules 30 followed by more thorough and accurate confirming checksof the initial estimate. Further, because each time series ofmeasurements for a given path 36, 38, 40, 42, 44, and 46 over some timeperiod can be treated statistically, the model can include a statisticalconfidence interval associated with the location of each turbule 30.Also, processing efficiency can be achieved by only comparing the paths36, 38, 40, 42, and 46 that intersect over a given region and by notprocessing those path intersections that occur above the troposphere 32or within the surface boundary layer.

Once the processor 264 builds (or modifies) the model, the network 262can be used to distribute the model. Preferably, the network 262includes a publisher-subscriber architecture that enables entities onthe network 262 to subscribe to the model with the processor 264 servingas the publisher. In this manner, bandwidth requirements fordistributing the turbulence model can be limited without compromisingthe quantity or quality of information being made available to thesubscribers 272. Additionally, the model can be segmented according topre-selected geographic areas over which the turbulence 30 occurs sothat the subscribers 272 can subscribe to geographic subsets of theoverall information contained in the model. The presence of GPSequipment already onboard many of the subscribers (e.g. aircraft thatmight also be measurement nodes) makes the implementation of locationbased subscription services easily achievable over the network 262.Additionally, conventional air-to-ground bidirectional communicationsystems (e.g. radios) can be used to relay turbulence relatedinformation between the components of the system. Thus, warnings ofturbulence can be transmitted from the ground to aircraft in thevicinity of the turbulence other than the aircraft that measured theturbulence. If the aircraft that measured the turbulence might beaffected by the turbulence onboard systems can communicate theturbulence information to the aircrew, or autopilot, so that appropriateevasive action can be initiated.

One type of subscriber 272 of particular interest is the Air TrafficControl (ATC) system 274 of the United States and its counterparts inother nations. The turbulence model can be distributed to the ATC system274 where it can be further distributed to the Control Centers and AirTraffic Control Towers (ATCTs) for use in controlling air traffic.Another exemplary subscriber 272 is the National Weather Service whichcan make use of the model for predicting severe weather. In otherpreferred embodiments, the subscribers 272 can include display devicesthat allow tomographic turbulence information to be overlaid onnavigation displays.

In other preferred embodiments, the processor can augment the model withdata from other sources. For instance, the meteorological model 264 canprovide estimates of the turbulence in volumes of the atmosphere wherethe signal paths between the transmitters and receivers have not sweptfor some time. Also, each aircraft (or mobile platform) thatcommunicates with the system 200 will typically be outfitted with airdata sensors 266. Because the air data sensors provide contemporaneous,localized, turbulence measurements, the air data sensors 266 canconfirm, or augment, the information in the turbulence model. Anotherexemplary source of information is the inertial sensors 270 onboard themobile platforms. Again these sensors 270 directly and contemporaneouslymeasure turbulence that the system otherwise senses remotely. Likewise,the system 200 can augment the turbulence model with meteorologicalinstruments 268 (e.g. weather stations) in areas prone to infrequentsignal sweeps. Thus, the collection of sensors 266, 268, and 270 can beused to calibrate and adjust the model in addition to merely augmentingthe information distributed via the model.

With reference now to FIG. 4, a method 310 in accordance with theprinciples of the present disclosure is illustrated. Generally, themethod 310 includes receiving electromagnetic energy that has beenaltered by turbulence, detecting the alteration caused by theturbulence, and building a three-dimensional model of the turbulence.More particularly, FIG. 4 shows the energy being transmitted inoperation 312 and encountering turbulence in operation 314 as itradiates from the transmitter. Because of the turbulence, the phase orthe frequency of the energy shifts, or fading or enhancement occurs tothe energy, as shown by the alteration in operation 316. In operation318, the altered energy is received. Operations 324 and 326 show thereceiver being moved and reoriented respectively while its heading andlocation are determined in operation 324. The alterations to theelectromagnetic energy are shown as being detected in operation 322.Operation 328 shows ionospheric scintillation being filtered from thesignal. Likewise, operation 330 removes the effects of receiver motionfrom the turbulence measurement. In operation 332 the direction,location, and time at which the energy was received are associated withthe measurement of the turbulence. If the turbulence was measured atmore than one location or time, the measurements can be correlated as inoperation 334. Once enough measurements of the turbulence are gatheredto allow for a statistically meaningful model (as indicated by operation336), a three-dimensional model of the turbulence is created inoperation 338. Additionally, the model can be augmented with otherrelevant information such as meteorological data or meteorologicalpredictions in operation 340. Further, the turbulence model can bedistributed to end users as shown by operation 342.

The embodiments were chosen and described in order to best explain theprinciples of the disclosure and its practical application to therebyenable others skilled in the art to best utilize the disclosure invarious embodiments and with various modifications as are suited to theparticular use contemplated.

As various modifications could be made in the constructions and methodsdescribed and illustrated without departing from the scope of thedisclosure, it is intended that all matter contained in the descriptionor shown in the accompanying drawings shall be interpreted asillustrative rather than limiting. For example, instead of merelyavoiding turbulence, the detected turbulence can be used to advantage.In one exemplary embodiment, a mobile platform is positioned on theopposite side of the turbulence from a laser device to protect themobile platform from the laser. Similarly, the mobile platform canmaneuver so that a laser on board the mobile platform can hit a targetdespite the presence of the turbulence. Thus, the breadth and scope ofthe present disclosure should not be limited by any of the exemplaryembodiments, but should be defined in accordance with the claims andtheir equivalents.

1. A method of predicting turbulence comprising: receivingelectromagnetic energy that has traveled along a path subject to theturbulence, the turbulence altering the electromagnetic energy;determining a first alteration of the electromagnetic energy caused bythe turbulence by filtering the electromagnetic energy as it wasreceived along a first path of travel by a first mobile platformcarrying a first receiver, at a first location, by using a velocity ofone of a transmitter of the electromagnetic energy or the first receiverthat received the electromagnetic energy; determining a secondalteration of the electromagnetic energy caused by the turbulence byfiltering the electromagnetic energy as it was received along a secondpath, non-parallel to the first path, by a second mobile platformcarrying a second receiver, and operating at a second location, by usingthe velocity of one of the transmitter of the electromagnetic energy orthe second receiver that received the electromagnetic energy; and usingthe determined first and second alterations to determine a zone wherethe turbulence is present and to create a three dimensional model of theturbulence in said zone.
 2. The method according to claim 1, furthercomprising determining a direction between the first receiver and thetransmitter.
 3. The method according to claim 1, wherein the velocitybetween one of the first receiver and the transmitter includes at leastone of a linear velocity or an angular velocity.
 4. The method accordingto claim 1, the turbulence including an ionospheric turbulence and atropospheric turbulence, the method further comprising using at leastone of the first and second receivers to determine a portion of thealteration of the electromagnetic energy caused by the troposphericturbulence.
 5. The method according to claim 1, wherein using the firstand second alterations to determine a zone where the turbulence ispresent comprises correlating the first alteration of theelectromagnetic energy and the second alteration of the electromagneticenergy.
 6. The method according to claim 5, further comprising thecorrelating including accounting for a time difference between thereceiving of the electromagnetic energy at the first location and thereceiving of the electromagnetic energy at the second location, the timedifference being defined by the velocity and a distance between thefirst location and the second location.
 7. The method according to claim1, the receiving the electromagnetic energy by the first and secondreceivers further comprising being from a satellite.
 8. The methodaccording to claim 1, the determining the alteration of theelectromagnetic energy by at least one of the receivers furthercomprising detecting at least one of a phase difference, an intensitydifference, or a frequency difference.
 9. The method according to claim1, further comprising distributing the three dimensional model via anetwork.
 10. The method according to claim 1 further comprising at leastone of subscribing to or publishing the three dimensional model.
 11. Themethod according to claim 1, further comprising determining astatistical confidence interval associated with the three dimensionalmodel.
 12. The method according to claim 1, further comprisingaugmenting the three dimensional model with a meteorological prediction.13. The method according to claim 1, further comprising collectingturbulence data with a sensor in the turbulence and augmenting the threedimensional model with the data.
 14. The method according to claim 1,wherein the turbulence is associated with an airport.
 15. A method ofpredicting turbulence comprising: receiving electromagnetic energy thathas traveled along a path subject to the turbulence, the turbulencealtering the electromagnetic energy; determining the alteration causedby the turbulence by filtering the electromagnetic energy as it wasreceived with a velocity of one of a transmitter of the electromagneticenergy or a receiver that received the electromagnetic energy; andcreating a three dimensional model of the turbulence.
 16. The methodaccording to claim 15, wherein the three dimensional model is atomographic model.
 17. A method of predicting turbulence comprising:receiving electromagnetic energy that has traveled along a path subjectto the turbulence, the turbulence altering the electromagnetic energy;determining the alteration caused by the turbulence by filtering theelectromagnetic energy as it was received with a velocity of one of atransmitter of the electromagnetic energy or a receiver that receivedthe electromagnetic energy; the velocity including at least one of alinear velocity or an angular velocity; determining a direction betweenthe receiver and the transmitter; and creating a three dimensional modelof the turbulence.